The role of arbuscualr mycorrhizae in inducing resistance to drought and salinity stress in crops

Abstract

Arbuscular mycorrhizal (AM) fungi are commonly occurring soil microbes whose association with roots can have wide ranging effects on growth of the host plants. These fungi are frequent root colonizers of trees, shrubs, terrestrial orchids and a broad range of plants in temperate and tropical habitats. During the establishment of AM symbiosis, a range of chemical and biological parameters are affected in plants. These fungi are considered instrumental in promoting plant establishment and growth in these environments by enhancing plant nutrient and water uptake, protecting plants from root herbivores and pathogens and improving soil structure. This symbiosis is alleged to improve plant resistance to drought and nutrient stress. There are several reports which show that AM induce physiological drought tolerance, involving both increased dehydration avoidance and dehydration tolerance. Majority of the experiments have shown that when the symbiosis improves host drought resistance it does so by aiding drought avoidance. AM symbiosis has frequently increased resilience of host plants to salinity stress. The AM plants in the saline soils had increased phosphate and decreased Na concentrations in shoots compared to non-AM ones. Salt resistance has been shown to improve by AM colonization in a number of crops like maize, mungbean, clover, cucumber, lettuce, tomato, and many more. A correlation has been established between AM colonization and improved osmoregulation or proline accumulation. AM colonization has also been documented to improve NaCl resistance in tomato, with the extent of improvement related to salt sensitivity of a cultivar. AM improvement of salt resistance has usually been associated with AM-induced increases in P acquisition and plant growth. However, there are scanty reports of AM induced effects on host plants being more pronounced when plants were exposed to osmotic stress in salinized soils.